Spent Coffee Grounds as a Lubricant in Pelleting of Wood

ABSTRACT

Pellets and a process for producing pellets are disclosed. The process includes recovering spent coffee grounds from a coffee production facility. The coffee grounds are then subject to a drying process to remove moisture from the coffee grounds to form dried coffee grounds. A mixture of about 0.5-5% dried coffee grounds and wood material is then formed. The mixture is then compressed in a pellet mill to form wood pellets including about 0.5-5% coffee grounds. The coffee grounds in the wood material acts as a lubricant for the pelleting machinery and eliminate the need for other lubricants in the process.

FIELD OF THE INVENTION

The present disclosure relates to a process for producing wood pellet,and, in particular, to a process for using a minor amount of dried spentcoffee grounds as a lubricant in the pelleting process.

SUMMARY

A process is disclosed for producing pellets in pelleting machinery. Theprocess includes recovering spent coffee grounds having a moisturecontent of about 50% directly from a coffee production facility. Thecoffee grounds are then subject to a drying process to remove moisturefrom the coffee grounds to form dried coffee grounds having a moisturecontent of 10% or less. A mixture of about 1-5% dried coffee grounds and95-99% wood material is then formed. The blend of wood material and thedried coffee grounds have a moisture content of from about 8% to 14%.The mixture is then compressed in a pellet mill to form wood pelletsincluding about 1-5% coffee grounds. The coffee grounds in the woodmaterial acts as a lubricant for the pelleting machinery and eliminatethe need for other lubricants in the process.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a pelleting system.

FIG. 2 is a flow chart illustrating the process of the presentdisclosure.

DETAILED DESCRIPTION

In general, wood pellets are a renewable energy carrier which isproduced from sawdust or other ground woody materials. Internationalstandards define product requirements i.e. moisture, energy density,abrasion resistance, particle size and shape for wood pellets (ISO17225-2) which allowed wood pellets to turn into a commodity.

There are different pellets from different sources and qualitiesavailable today, such as wood pellets, animal feed pellets, torrefiedpellets etc. Wood pellets of dedicated qualities are dominating and aredelivered and consumed in two different markets: (1) In the electricitygeneration sector, they are co-fired in coal-based power plants andmono-fired in converted coal power plants to reduce greenhouse gasemission of electricity generation. (2) In the residential heatingsector, they are widely used as a convenient solid biofuel applicationin automatic stoves and boilers. Therefor pellets with a dedicatedquality are dominant, which are produced closer to the consumer andcharacterized by trade within the country or between neighboringcountries. Delivery is realized in small scale units in the retailmarket and in large scale or bulk units in the power generation market.

Additional applications for the use of wood pellets are the use as fuelfor mid-sized heat supply systems, such as district heating and CHPplants. Generally, pellets may be used for commercial/residential use orfor industrial use. The majority of non-industrial, mostly heat marketpellets traded are A1 quality, which are rated for residential heatsupply.

As is known in the art, pelleting takes a finely divided, sometimesdusty, unpalatable, and generally difficult-to-handle feed material and,by use of heat, moisture, and pressure, forms the material into largerparticles (pellets). These larger particles are easier to handle, morepalatable and usually result in improved results when compared to theunpelleted feed or fuel Pellets may be formed with diameters from 10/64″to 48/64″ and will be somewhat longer than their diameter. In someembodiments, pellets may be cylindrical, triangular, square or oval.

Typically, a pelleting system is composed of several different machinesdesigned to most efficiently accomplish the pelleting task. A typicalsystem arrangement with equipment names is shown in FIG. 1. Initially,the pelleting process starts with a bin 10 in which the mixture to bepelletized is stored. The mixture then flows by gravity into the pelletmill 20 where pellets are formed. Hot extruded pellets are subsequentlytransferred by gravity into a cooler 25 where they are held while beingcooled and dried by a flow of air. The air is drawn through the mass ofpellets and passed into a dust collecting device, such as a cyclonecollector 30. The dust from the outlet of the collector 32 is returnedto the pellet mill 20 to again be compacted into a pellet. From thecooler 25, the product flows through or around a pair of crumble rolls35. From the crumble rolls 35 the product flows into a bucket elevator40 to be raised to a higher point in the structure where the shaker 45is located. The shaker 45 separates the product into various sizes bypassing the material over several screens. Each screen is of a differentmesh size. This separation permits the desired product to be separatedfrom the larger or smaller particles while being delivered to thefinished product bin. The fines can be returned to the pellet mill forre-pelleting or, in the case of crumbles, to the cooler, where they arereturned to the crumble rolls for re-crumbling. The fines or smallermaterial can be routed directly back to the pellet premix bin andreprocessed through the pelleting system.

In a typical pelleting operation, the mixture flows by gravity into thepellet mill die chamber where rollers press the softened mash throughthe holes in a circular die. Stationary knives located outside thecircular rotating die, cut off the shaped dense pellet at the properlength. Most modern pellet mills used a ring type die that turns abouttwo fixed rollers, with the die and rollers mounted in a vertical plane.A few mills are built with the dies and rollers in a horizontal planewith the rollers turning within the stationary die. In the pelletingunit, the conditioned mash is forced through holes in the die by rollerpressure. Die thickness is a factor in the production of high qualitypellets and must be accurately balanced with the formulation andconditioning. Starting with 24/64 inch pellets and above, some variationin the amount and depth of taper incorporated into the entry of theholes in the die may be necessary. Numerous other special entries areused in instances where satisfactory pellets cannot be produced withstandard entry and taper.

Pellet mills generally incorporate some type of speed reduction device,since die speeds are less than the conventional motor speeds. In somecases, variation in die speed is desirable to produce optimum resultswith respect to individual groups of feeds. Speed reduction devices inuse today include direct coupled gear trains, V-belts, cog belts, aswell as combinations of belts and gear trains. Currently, mills arebeing built with speed change mechanisms. Usually these speed changemechanisms are in the form of gear shifts or two-speed motors. Suchmills provide two die speeds to secure optimum results when a wide rangeof feeds is produced.

Most pellet mills are installed with an electric motor as the primemover; however, internal combustion engines are sometimes used. Wheninternal combustion engines are used, the horsepower rating should be atleast twice that of the electric motor normally used. The pellet milland motor are usually mounted on a common base to maintain alignment ofthe pellet mill and motor and to provide a rapid, simple and efficientmethod of installing the equipment. Although it is not a standard partof the pellet mill, an ammeter should be included as part of theelectrical system. This will allow the operator to adjust the feed rateto secure the maximum capacity of the mill without overloading themotor. In the production of wood pellets, the mixture is fed through apellet mill using either a flat die or a ring die compression system.

During the pelleting process, friction can occur due to the differencein temperature of the feed entering the pellet mill die and the pelletsbeing discharged from the die. The difference reflects the mechanicalenergy required to produce a pellet. There are several inherent factorsthat can affect friction including moisture in the mixture,conditioning, particle size of the mixture ingredients, physicalproperties of the mixture ingredients, including mineral content,solubility, and fiber content. Additionally, friction can resultaccording to the die size in terms of mesh diameter and thickness.Further, pelleting of woody material creates friction in the die itself,which in turn can create significant heat during the pelleting processand which becomes a limiting factor in the rate at which pellets can beproduced. In certain cases, organic and/or petroleum-based materials(lubricants) are added in small quantities to the woody feedstock inorder to facilitate the pelleting process, thereby reduce thefriction-based heat, and increasing the overall rate of pelletproduction.

The addition of dried spent coffee grounds (SCG) has been found to be asuitable lubricant for reducing friction in the pelletizing process. SCGcontain a significant amount of natural organic oils which contain bothhigh BTU content as well as significant lubricating properties. When SCGare premixed with woody biomass prior to pelleting in amounts from 0.5%by weight to 5% by weight, significant lubrication of the pelletingprocess occurs. Binders may or may not be included with the woodybiomass. Because of the reduced friction imparted by the SCG, lower heatproduction during the process may be realized. In addition, pelletproduction rates have been found to increase by up to 30% overconventional pelleting processes, using conventional lubricants. Driedcoffee grounds are particularly useful as a lubricant in the pelletproduction process for both flat die and ring die production.

As shown in FIG. 2, coffee arrives at a receiving station 50 of a dryingfacility from a coffee facility and enters a fluidized bed dryer 60 at30% to 60% moisture. The drying facility includes a receiving dock,burners, dust collectors, a bagging station, and silos for storing thedried coffee grounds. Dust collection 70 allows excess material to beproperly ventilated while the dryer is operating. Following drying toabout 10% moisture, the dried coffee grounds are stored in silos inpreparation for bagging, as shown at 80. The material is thentransferred to sacks 90 and loaded for transportation 100 to apelletizing facility. The dried coffee grounds are then placed in amixer along with wood for pelletizing 110. The mixture then enters thepellet mill 120, which operates more efficiently due to the lubricatingproperties of the coffee grounds.

One example of dried coffee grounds suitable for the process is:

Date/Time Analytical Test Results Units MQL DF Analyzed By Method LabNo: 96949 Sample ID: Dried Coffee Metric: Solids Sampled: Moisture 5.00% 0.10 1 06/07/18 14:15 AOAC 930.15 Dry Matter 95.0 % 0.10 1 06/07/1814:15 CLF AOAC 930.15 Crude Protein 10.9 % 0.1 1 06/07/18 17:15 CLF AOAC990.03 Crude Fat 26.4 % 1 06/07/18 11:52 RLF AOAC 920.39 Lab No: 96950Sample ID: Dried Coffee A Metric: Solids Sampled: Moisture 5.00 % 0.10 106/07/18 14:15 AOAC 930.15 Dry Matter 95.0 % 0.10 1 06/07/18 14:15 CLFAOAC 930.15 Crude Protein 10.8 % 0.1 1 06/07/18 17:19 CLF AOAC 990.03Acid Detergent Fiber 75.4 % 0.100 1 06/07/18 12:01 RLF AOAC 973.18Neutral Detergent Fiber 77.1 % 0.100 1 06/07/18 12:13 RLF NDF TotalDigestible Nutrients (TDN) 41.2 % 0.100 1 06/07/18 12:01 RLF AOAC 973.18Estimated Net Energy (ENE) 22.0 ton/cwt 1 06/07/18 12:01 RLF AOAC 973.18Net Energy Lactation (NEL) 0.406 Mcal/lb 1 06/07/18 12:01 RLF AOAC973.18 Net Energy Maintenance (NEM) 0.314 Mcal/lb 1 06/07/18 12:01 AOAC973.18 Net Energy Gain (NEG) 0.084 Mcal/lb 1 06/07/18 12:01 AOAC 973.18Calcium 0.07 % 1 06/07/18 11:26 CLF FEED METALS Phosphorus 0.01 % 106/07/18 11:26 CLF FEED METALS Potassium 0.05 % 1 06/07/18 11:26 CLFFEED METALS Magnesium 0.01 % 1 06/07/18 11:26 CLF FEED METALSQualifiers/Definitions DF Dilution Factor MQL Method Quantitation Limit

In this embodiment, the amount of dried coffee grounds used in the woodmay be 1%, 2.5% or 5% and the moisture content is between 5-15%, but maybe as low as 3%. Since the coffee is substantially rich in oils, driedcoffee grounds have been found to improve the efficiency of pelletingmachinery at relatively low amounts in the mix. Thus, the machine isless likely to buckle, or knock during the pelleting process when coffeegrounds are added to the wood material.

Not only does the coffee affect the final product by helping thematerial flow through the pellet machinery in a quicker fashion, thesmall amounts of coffee result in some increase in the BTU levels of thefinished product because dried coffee grounds have a BTU content perunit of mass approximately 30% higher than the wood feedstock.

Changes and modifications of the preferred embodiments described abovewill become apparent to persons skilled in the art. The scope of theinvention is therefore intended to be limited solely by the scope of theappended claims.

1. A process for producing pellets using coffee grounds as a lubricant,comprising: providing coffee grounds having an initial moisture content;drying the coffee grounds to a second moisture content of 3-15%, byweight; forming a mixture of about 0.5-5%, by weight, dried coffeegrounds and about 95-99%, by weight wood material, said mixture having athird moisture content; compressing the mixture in a pellet mill to formpellets including wood material and about 0.5-5%, by weight, coffeegrounds, wherein the coffee grounds act as a sole lubricant in theprocess for producing pellets.
 2. (canceled)
 3. (canceled)
 4. Theprocess of claim 1, wherein the coffee grounds are dried to the secondmoisture content of about 10% or less, by weight.
 5. The process ofclaim 1, wherein the third moisture content is about 8% to 14%, byweight.
 6. (canceled)
 7. The process of claim 1, wherein the pellets areextruded through a die to form pellets having a diameter of 10/64 inchesto 48/64 inches.
 8. The process of claim 7, wherein the pellets aresubsequently transferred by gravity to a cooler where the pellets arecooled.
 9. The process of claim 8, wherein air is drawn through thepellets and passed to a dust collection device.
 10. The process of claim9, wherein fines are routed back to the mixture for reprocessing. 11.The process of claim 1, wherein the process further includes a step ofadding a binder to the mixture and the pellets further includes abinder. 12-20. (canceled)
 21. The process of claim 1 wherein the pelletmill includes an ammeter to allow for adjustment of a feed rate tosecure a maximum capacity of the pellet mill without overloading amotor.
 22. A process for producing pellets using coffee grounds as alubricant, comprising: providing coffee grounds having a moisturecontent of about 3-10%, by weight; forming a mixture of about 0.5-5%, byweight, coffee grounds and about 95-99%, by weight of a wood material,said mixture having a moisture content of about 8% to 14%, by weight;compressing the mixture in a pellet mill to form pellets including woodmaterial and about 0.5-5%, by weight, coffee grounds, wherein the coffeegrounds act as a sole lubricant in the process for producing pellets.23. (canceled)
 24. The process of claim 22, wherein the process furtherincludes a step of adding a binder to the mixture and the pelletsfurther includes a binder. 25-26. (canceled)
 27. The process of claim 22wherein the pellet mill includes an ammeter to allow for adjustment of afeed rate to secure a maximum capacity of the pellet mill withoutoverloading a motor.